The present invention relates to a plain bearing for connecting rods, which is mounted on an end of a connecting rod, more particularly the plain bearing which can enhance rigidity of the connecting rods.
For example, in engines of motor vehicles, a wrapped bush type plain bearing with a small diameter is mounted on the small end of a connecting rod to receive a piston pin, and a hemi-circular plain bearing with a large diameter is mounted on the big end of the connecting rod to receive a crank pin.
Such a connecting rod has been usually made of steel and has high rigidity. On the other hand, recently, in engines of race cars and high-speed/high-power engines of a part of usual cars, connecting rods have been made of a light metal alloy, such as titanium or aluminum, in order to make the engines lighter. However, because the connecting rod made of a light metal alloy has lower rigidity than steel one, it is comparatively flexible, especially at the big end thereof which receives a large diameter plain bearing, whereby the plain bearing, which receives a crank pin, may be damaged.
Specifically, because the connecting rod transforms the reciprocating movement of a piston into the rotational movement of a crankshaft, compression and tensile loads are alternately exerted on the big end of the connecting rod. Thus, the big end 1 is deformed by the alternate dynamic load so as to be elongated and compressed in the longitudinal direction of the connecting rod as shown in FIG. 6 in which the deformation of the big end is exaggeratedly shown. When the big end 1 is deformed as shown in FIG. 6, two hemi-circular bearing halves 3 and 4 of a plain bearing 2 for a crank pin are also deformed, whereby the butted ends of the bearing halves 3 and 4 are constricted so as to protrude radially inwardly. This is so called xe2x80x9ca closed in statexe2x80x9d. When the xe2x80x9cclosed in statexe2x80x9d occurs, edges xe2x80x9cAxe2x80x9d of crush relief sections 3a and 4a, which are provided to the bearing halves 3 and 4 adjacent at the circumferential ends, respectively, butt locally against a crank pin 5, so that a seizure occurs and/or the bearing halves 3 and 4 move relatively to the big end 1 with a slight amplitude bringing about a fretting phenomenon therebetween or occasionally a fracture of the connecting rod.
Further, when the big end 1 is deformed as described above, clearances between the crank pin 5 and the plain bearing 2 (i.e. the bearing halves 3 and 4) becomes larger longitudinally with respect to the connecting rod. Therefore, the crank pin, which evolves with a high speed, moves relatively and heavily to and within the plain bearing 2 in the longitudinal direction (i.e. upwardly and downwardly in FIG. 6) bringing about cavitation to corrode the bearing surface.
The present invention has been proposed under such technical backgrounds.
An object of the invention is to provide a plain bearing for connecting rods, which can reinforce the connecting rods to improve rigidity thereof.
Under the object, according to a first aspect of the invention, there is provided a plain bearing for connecting rods, which is mounted in an end of a connecting rod and which comprises a cylindrical bearing body and a flange which is provided on an axial end of the bearing body so as to extend along at least a quarter of the circumference of the axial end and projects radially outwardly.
According to this feature, when the plain bearing is mounted on a connecting rod, the latter is reinforced to have improved rigidity as a whole including the plain bearing, whereby, even if the connecting rod is made of a light metal alloy, it is hardly deformed and can effectively prevent seizure of the plain bearing, and occurrence of fretting and cavitation phenomena.
According to a second feature of the invention, the flange is provided on the respective axial ends, so as to extend along the overall circumference of the respective axial ends. According to this feature, the plain bearing can have still higher rigidity as compared with a case of a flange provided only on any one of the axial ends or provided so as to extend along a half of the circumference of the axial end(s).
According to a third feature of the invention, the bearing body comprises a back metal and a bearing alloy layer formed on the back metal, wherein the flange is integrally formed with the back metal by bending the corresponding axial end radially outwardly. According to this feature, the flange is comparatively easily provided to the plain bearing thereby saving the production cost.
According to a fourth feature of the invention, the flange is provided on the axial end by integrally securing a separate flange member to the bearing body. According to this feature, the thickness and/or width of the flange can be optionally determined irrelevantly to the bearing body thereby enhancing still higher the rigidity of the plain bearing as a whole.